For simplicity sake, I'm going to assume a 3 player game (1P, 2P, OP), each player is at 40 life, and all other creatures in play are vanilla bears (A through D). Arcbond and Spiritualize have already finished resolving, and we're now casting Warleader's Helix onto an empty stack, targeting ITN.
Format: Name (Target/Origin) - Effect
Cast Warleader's Helix, targeting ITN
Stack
Warleader's Helix (ITN) - 4 damage, gain 4 life.
ITN's ability triggers, producing a copy for each other creature.
Stack:
Warleader's Helix (ITN) - 4 damage, gain 4 life.
Warleader's Helix (BearA) - 4 damage, gain 4 life.
Warleader's Helix (BearB) - 4 damage, gain 4 life.
Warleader's Helix (BearC) - 4 damage, gain 4 life.
Warleader's Helix (BearD) - 4 damage, gain 4 life.
Warleader's Helix resolves against BearD, dealing 4 damage. OP gains 4 life. Arcbond applies it's triggers.
Stack
Warleader's Helix (ITN) - 4 damage, gain 4 life.
Warleader's Helix (BearA) - 4 damage, gain 4 life.
Warleader's Helix (BearB) - 4 damage, gain 4 life.
Warleader's Helix (BearC) - 4 damage, gain 4 life.
Arcbond (BearD) - 4 damage to each other creature and player.
BearD is put into the GY as a state based action. Arcbond(BearD) trigger resolves, dealing 4 to each player and triggering Arcbond but not Spiritualize (Spiritualize stops affecting BearD when it leaves play).
Stack
Warleader's Helix (ITN) - 4 damage, gain 4 life.
Warleader's Helix (BearA) - 4 damage, gain 4 life.
Warleader's Helix (BearB) - 4 damage, gain 4 life.
Warleader's Helix (BearC) - 4 damage, gain 4 life.
Arcbond (BearA) - 4 damage to each other creature and player.
Arcbond (BearB) - 4 damage to each other creature and player.
Arcbond (BearC) - 4 damage to each other creature and player.
Arcbond (ITN) - 4 damage to each other creature and player.
All remaining creatures are sent to the GY as a state based action. Arcbond (ITN) resolves next, dealing 4 damage to everything, as with Arcbond (BearA;BearB;BearC). The remaining Warleader's Helix copies/original fizzle without legal targets, and thus OP gains no life.
End Result:
Board clear
OP life total = 24
1P/2P life total = 20
If anything had high enough toughness to survive the 4 damage from the first Arcbond/WH, then OP would be able to gain a good chunk of life. Best case scenario would be to put the Warleader's Helix targeting the highest toughness monster on the top of the stack, to gain the most life.